The present invention relates to an electrical interrupter for a capacitor coil. Such an interrupter is disclosed in FRG Pat. No. 2,350,271 and GB Pat. No. 1441507.
In this prior art arrangement gas formation in dielectric material is utilized when there is undue heat development due to a defect or fault in the capacitor coil. A breakable or tearable conductor applied to a surface of the capacitor coil bulges out when there is excess pressure in the coil interior so that the conductor is interrupted by such excess pressure. This requires that the covering of the capacitor coil itself not be deformed by the excess pressure.
In a defined zone within the casing, which acts as a pressure vessel and remains intact even in the case of a defect, a desired break location is provided at the capacitor coil in the form of a plate of insulating material equipped with grooves or notches. This plate supports a breakable conductor in the form of a glued-on metal foil or a vapor-deposited metal layer.
On the side of the plate of insulating material facing away from the capacitor coil, an elastic material is provided within the casing which enables the plate of insulating material to be pressed into this elastic material when the capacitor coil bulges out under the pressure of the gas. This causes the plate of insulating material to break and thus the conductor to be interrupted. Due to this interruption, the circuit leading through the conductor from external terminals of the capacitor is switched off.
In those cases in which the capacitor coil is wound of a metallized plastic sheet, generally no gas develops in the case of a defect to produce excess pressure which would actuate the interrupter. The partial surface enlargement of the capacitor coil occurring in the case of a defect may become active, in contrast to gas pressure, at a location at which there happens to be no plate of insulating material and no breakable conductor so that the prior art arrangement often fails in such cases.
German Pat. No. 1,289,584 discloses a capacitor having an interrupter which breaks under excess pressure. In this case, a capacitor coil in insulating oil is installed in a housing which is able to expand in the direction of the coil axis. In the case of damage, overheating at the point of the defect produces heavy gas development which generates a pressure acting also in the direction of the coil axis, thus lengthening the housing at the point of expansion. This causes an internal connecting wire to break and to interrupt the current flow.
The prior art structures are costly in that in every case the capacitor coil must be installed in a suitable housing and additionally an impregnating agent is required to generate excess gas pressure in the case of a defect. Therefore, these solutions are not very well suited for capacitor coils which do not require impregnation, i.e. particularly for metallized sheet capacitors.